Vulcanized high-pressure polymers



Patented Dec. 18, 1945 ,7

UNl'lED srn'rss PATENT OFFICE 2.891.095 Q vuwamzsnman-raassunaronmns Henry 1:. Keller. Union on; and Per 1:. Irolieh.

Westiield, N. 1., aellsnoro to Standard Oil Development Company, a corporation of Delaware No Drawing. Application November 8, 1041, Serial No. 418,810

11 (i. zoo-79) This invention relates to the treatment with sulfur of the unsaturated interpolymerization products of high molecular weight which are prepared at high pressures from mixtures of monoolefins and other polymerizable organic compounds of relatively greater oleflnic unsaturation. It has especial application to the treatment with sulfur of high molecular weight interpolymerization products of ethylene with other polymerizable organic compounds having polyoleflnic unsaturation which are obtained by the treatment of a mixture of ethylene and such polyoleflnic compounds at high pressures, generally above about 500 atmospheres.

One object of this invention is to provide novel sulfur-containing interpolymeric materials with physical properties similar to rubber and which are suitable for use as rubber substitutes in numerous applications. Other and further objects will be apparent from the following description and the claims.

It is known that semi-solid and solid waxlike polymers of ethylene having high molecular weights of at least 2,000 are obtained by subjectingethylene to veryhigh pressures of the order of 500 to 1500 atmospheres, preferably in the presence of traces of oxygen. at temperatures below about 400 C. and preferably between about 100 C. and 250 C., with careful control of the reaction temperature and with provisions for removing the large amounts of heat liberated in the reaction in order to avoid exceeding the desired temperature in the reaction zone. Such polymers are substantially saturated in character and react only very slightly, if at all, with sulfur. Similar interpolymers or copolymerization products of a high degree of saturation are obtained by the treatment of mixtures of ethylene with other unsaturated hydrocarbons having a single olefinic linkage.

According to the present invention,.a mixture 1 of a suitable mono-olefin, such as ethylene with a polyoleiine (containing at least two double bonds of the, olefinic type per molecule) is subiected to similar high .pressure polymerization treatment with the production of high molecular weight semisolid or solid interpolymerization products or 'copolymers. These products have a substantially higher degree of unsaturation of such a nature that they can be caused to react with sulfur to form desirable rubber-like materials.

The mixture to be subjected to the'hlgh pressure polymerization treatment should'contaln at least 75% (molal basis) of ethylene and about 55 he cti 1% to 25%, preferably about 2%.to 5% or'-l0%, of polyoieflnic materials.

In place of ethylene, other mono-oleflns prefene may also be used. Dlvlnyl benzene and other I with the ethylene, and/or relatively inert madivinyl compounds are also suitable. Cyclic polymerizable diolefines such as cyclopentadiene, and the like, the dioleflns of four to six carbon atoms are preferred, although other diolefins and organic compounds containing two, three or even more oleflnlc linkages in the molecule may also be used.. Mixtures of two or more of such dioleflns and polyolefinic materials may also be used to prepare mixed interpclymerizates with the ethylene. The remainder of the mixture may consist of other oleflns or preferably three to six carbon atoms which may also interpolymerize terials, such as the normally gaseous parafllns, nitrogen and like inert gases. The presence of a small amount of oxygen, above about 0.01%, and preferably between about 0.03% and 0.1%, is also desirable as this greatly reduces the pressure at which the reaction may be conducted. Somewhat larger amounts of oxygen may be used but care should be taken to avoid the presence of sufllclent oxygen to create an explosive mixture.

The inter-polymerization ofsuch mixtures is accomplished by subjecting them to high pressures of the order of 1,000 to 1,500 atmospheres or higher and the highest attainable pressures of 15,000 atmospheres or more may .be used. The lnterpolymerizatlon may also be conducted at lower pressures of the order of 500 atmospheres or less when free oxygen is present in the amounts indicated above or when reactive materials capable 'ofsupplying oxygen in similar amounts, such as the inorganic and organic peroxides, e. g., benzyl peroxide, are used. Even lower pressures of the order of atmospheres readily polymerizable conjugated diinclude the ai maybe used with v olcflns in about to concentration. The

. mixture of reagents is held at the reaction pressure for a time sufficient to cause the reaction .to

I proceed to the-desired extent, which varies from a few minutes to a considerable number of hours,

depending upon the amount of oxygen or other catalyst used, and the reaction temperature, which ranges from about room temperature to about 300 or 400 0.;1'reaction temperatures between about 100 and 200 C. being generally preferred. There are thus obtained copolymers or interpolymerization products having molecular weights above about 2,000 and generally of, about 10,000 to 30,000 or more. The higher molecular weight products may be obtained by subiecting 'the poly- :merization products to distillation under high vacuum or by extraction with suitable solvents to elastic products.

low enough molecular weight to have the conconsisting substantially of ethylene or other remove materials of relatively lower molecular weight.

flhe degree of unsaturation of these interpolymerization products is dependent uponthe bf diolefin or other polyolefln entering the reaction and may be closely controlled by adjustment of the proportions of the initial reagents;

.lihes interpolymerization products may be cured according to the present invention so as to completely saturate the substance chemically without'converting it into a hard resin. as occurs when rubber is thoroughly saturated with sulfur. That is; sulfur may be applied to the internolymer in a proportion sumcient to saturate the interpolymer completely while retaining desired characteristics of elasticit hi h tensile strength.

elon ation and elastic limit, but if the same proportion of sulfur is applied to rubber. the rubber interpolvmerized materials combine with sulfur alone only with great dimculty and at elevated temperatures. in further shar distinction from rubber. Furthermore, the response of the materialto sul'fur-containing compounds to aid the curing or sulfurization reaction is greatly different from that of rubber. the best cures being obtained when very active accelerators are used such as thecarbamate and thiuram types.

The requirements of the interpolymerized ma tcrials for the obtaining of a satisfactory cure with sulfur to yield a maximum tensile strength and a maximum elasticity appear to-be detertion permitting curing of the interpolvmers is that corresponding to an iodine number of 1. The molecular weight 01' the interpolymers should be above a minimum value of about 10,000 to 15,000 in order to produce a material which can be cured to an elastic material with structural properties (freedom from cold flow), this mini.. mum molecular weight being required largely without regard to the amount of unsaturation in the molecule, although it varies to some extent with the amount of unsaturation. the materials of relatively high unsaturation, when cured with correspondingly large amounts of sulfur. equivalent to such unsaturation. being useful in relatively lower molecular weights than the more, sat-' urated interpolymers. Polymeric materials of mono-olefin but modified with small amounts of polyolefins, have a distinct advantage over the simple polymers of ethylene and the interpolymers of ethylene with mono-oleflns in that these latter cannot be cured or vulcanized in the ordinary sense of the term, whereas the ethylenelyolefln interpolymers can be cured-so as to have desirable characteristics of hardness, toughness, elasticity, etc. On the other hand, rubberlike polymers prepared largely or substantially to oxidation and attack by acids, ozone and other chemicals, even after curing. Moreover, such di-' olefin polymers have a low tensile strength in the cured pure gum form, whereas the cured products of the present invention have substantially higher tensile strength.

In the curing of the ethyiene-polyolefin polymeric material according to the present invention, it is possible to compound the polymeric material with sulfur, and by prolonged heating at a substantially elevated temperature, a cure can be obtained. Usually, however, this cure is not complete and is suitable for only a limited number of purposes. With sulfur alone. the rate of reaction between the sulfur and the copolymer is very slow and at the temperature required for this reaction, tie-polymerization and breakdown of the polymeric material occurs at such a speed that considerable injury is caused before a maximum cure is obtained. Because of this, it is highly desirable to incorporate into the polymeric material a suitable quantity of suitable cure aids and accelerators, including such substances as zinc ox= ide, stearic acid, the various sulfur compounds of thiuram and the alkyl dithiocarbamates, together with an appropriate amount of sulfur. An example of a suitable compounding formula is as follows:

Parts by weight Synthetic copoiymer (about 10,000 molecular weight, iodine number 5, prepared by high pressure inter-polymerization of ethylene and butadiene) lull Zinc oxide 5 Stearic acid 3 Sulfur 2 Tuads (tetramethyl-thiuram disulflde) i mixing operation, since otherwise a premature cure may occur on the rolls.

This compounded polymer produces what may be called a pure gum stock since it contains only a small amount of added material. Alternatively, a wide range of auxiliary substances, such 1 copolymers om! Wax Carbon black as inert pigments, organic fillers, clay,- carbon black, plasticizers and other substances may be added to modify the characteristics of the maprene,

butadlene,'etc., and are surprisingly inert to chemical reagents and solvents generally. such terial. A typical black stock formula is as above,

but with the addition of 50 parts .ofcarbon black.

The compounded interpolymeris preferably in molds, by the application of a temperature ranging from .about 125 to 1'15- C. or higher, up to 225- C., for a time interval ranging from about five minutes to 120minutes or more, according to the curing temperature, the charthen cured,

acter of the sulfur compound, the extent of cure desired, etc. 1 a v For some purposes, the curingis preferably carried out at a relatively low temperature, e. .g., between about 100 C. and 150 9., preferably about 120 C. to 130 6., or at a temperature at which a relatively long time, c. g.. four or five hours or more, ed to effect the curing.

is requir In other words, for some purposes, it is better to -'use a low temperature, long time curing treatment than to use a high temperature,

curing treatment. I

time and curing temperature'are markedly effected by the amount and nature of the sulfur aid or accelerator. Very active accelerators of the type of Tuads" and the alkyl dithiocarbamates are thus preferred, although curing under relatively more intensive conditions of temperature and time than required with these accelerators may also be obtained with other acshort time celerators. Examples of suitable accelerators are Tetramethyl thiuram disulflde Selenium tetraethyl dithiocarbamate zinc dibutyl dithiocarbamate In regard to the dithiocarbamate accelerators, the dialkyl dithiocarbamates are preferred.

The addition of the ethylene-polybutene interpolymers is often desirable in order to facilitate mixing and subsequent pr essin'g, as such interpolymers, especially those of high molecular weight ranges, are rather tough. Suitable softeners and plasticizers are coal tar, aromatic naphthas, waxes, both paraffin wax, mineral and vegetable waxes, tri-. cresyl phospha e, dibutyl phthalate, and the like. ding these copolymers, it is'generally Incompoun desirable to add such softeners and plasticizers among the first in order to aid the incorporation and distribution of the other ingredients in the copolymer composition.

An example of a such softeners and plasticizers is as follows:

Parts by weight Synthetic copolymer (about 10,000 molecular weight, iodine number 5, prepared by high pressure polymerization of ethylene and butadiene) Wood rosin Coal tar Tuads? u The cured copolymeric materials of the present invention are markedly superior in chemical resubstitutes as isoplasticizers and softeners to suitable formula including 7 a and particularly valuable method .of operation is still ethylene dichloride, mineral acids, oxygen per, manganese, cobalt and their salts). The resistance of these cured copolymers tothe effects of sunlight and to agin in the presence or absence of sunlight is also very The above presented formula contains various auxiliary substances which are desirable in small 4 characteristics of the cured copolymers but their unknown. Carbon constituent of the cured copolymerlc material. the abrasion resistance of this relatively harmless to its other physical properties. The cured polymeric materials of this invention may be loaded with a wide variety of pigments. For instance, fine particle size whiting and flne particle titanium dioxide may be .used as fillers in such large percenta es as and even over 200% of the weight of the copolymeric substance. Clay of the type known as Dixie clay may proportions up to about 50% onthe polymeric Zinc oxide hkewise may be used as a and the results are much the same as with'titanium dioxide. The asphaltic substance known as mineral rubber is likewise an excellent loading material. Particularly valuable described interpolymers are obtained in admixture with a wide range of other substances. These other substances particularly are the various isobutylene polymers,

known as Vistanex Polyoutene and also in admixture with the interpolymers of isooleflns and diolefins produced at low temperature. Both of these polymers can be admixed with the polymers of the present invention and .the mixture be cured with sulfur. With respect to the isoolefindiolefln low temperature interpolymers and the polymers obtained according to two curing reactions are sufficiently nearly alike to permit of the'preparation of mixtures of the tion aids and various fillers if desired, followed by the simultaneous curing of the two substances in admixture to produce particularly valuable elastic bodies, which are materially harder and of materially different elastic characteristics than are obtainable with other types of plastic and elastic substances. Similarly, the interpolymers of the present invention are particularly advantageous in admixture with the simple polymers of ethylene (Polythene) and with the interpolymers of ethylene and ene. This composition of matter valuable for electrical insulation very low dielectric losses, its

strength, and its advantageous dielectric constant. Similarly the interpolymers of the present invention admix readily with paraflin wax, and high pressure ethylene polymers, to produce compositions of matter having substantial strength I electrical properties. The materials also mix readily with rubber, and may be compounded therewith together with appropriate amounts of' sulfur and sulfurization is particularly because of its be used to advantange in as an aid to the curing compositions of the above both the simple viscous liquid and plastic solid polymers of isobutylene the present invention, the

mono-oleflnes such as isobutylhigh dielectric aids, and the rubber vulcanized and the polymers for a time sumcient to secure a viscous liquid to cured simultaneously by appropriate heat treatpl stic s li n p lymerization P d t n ment. Similarly the materials mix readily with thereafter heating said interpolymcr zat n p the various polybutadiene types of synthetic rubnot with sulfur and a sulfurization aid.

her, and with the similar interpolymers of buta- 3. Process according to claim 2 in which the diene and acrylonitrile or interpolymers of butacuring operation is conducted by heating the said diene and styrene both of which are prepared by interpolymerization product with sulfur and a the emulsion polymerization technique in which sulfurization aid at a temperature ranging from use also it imparts marked improvements in elec- 100 C. to 225 C.

tric'al characteristics and physical characteris- 1o 4. Process according to claim 2 in which the tics to the compound, especially in the presence curing operation is conducted by heating the said Of sulfur, a sulfurization aid and various amounts interpolymerization product with sulfur and a of solid pigment fillers. sulfurization aid ata temperature ranging from The cured copolymeric materials of this inven- 100 C. to 225 C. for a time ranging from 2 to 240 tion are of great value for electrical cable coat- 5 minutes.

' sheetin automobile tires, inner tubes, valves and go 100 C. to 225 C. for a time ran ng from 2 to24 accessories, such as motor supports, windshield minutes under pressure. 6. Process according to claim 2 in which said the cured copolymeric materials may be produced dioleiln has from 41:0 6 carbon atoms per molein a sponge-like form and employed for thermal cule.

insulation or shock-absorbing material. The 25 7. Proces according to claim 2 in which said cured copolymeric material of this invention is dioleiln is butadiene.

also of use when mixed either alone or in emul- 8. Process according to claim 2 in which said sion form with asphalt, waxes, cements, Portland diolefln is isoprene.

cement, etc., to waterproof and windproof ma- 9. Process according to claim 2 in which said SOnly composition boards and other permeable dioiefln ispiperylene.

structures. It is also suitable for use in sub- 10. Process according to claim 2 in which said marine cables, pump gaskets, wringer rolls, fire sulfurization aid is a sulfide of thiuram.

hose, steam gaskets, and as a coating or impreg- 11. Process according to claim 2 in which said hating agent for Cellophane, paper, pyroxylin suli'urization aidis tetramethyl thiuram disulflde. etc., in bottle and jar cap enclosures. vIt may be 5 2. ss according to claim 2 in which said used with cork fillers for shoe soles and comsulturization aidis a thiocarbamate.

pounded with asphalt as a laminating agent for 13. Process according to claim 2 in which said fabrics generally, whether woven, felted or laid sulfurization aid is a dialkyl dithiocarbamate.

tery cases, storage battery separators and acid 40 mers of ethylene comprising subjecting amixture tresses and seat springs, etc. 4 having substantial unsaturation and physical It is to be understood that there are presented characteristics ranging from those of a viscous herein but a limited number of embodiments of liquid to a plastic solid, and thereafter heating the structure of this material, that these are insaid inter-polymer with sulfur.

tended solely as illustrative examples and that 15. Process according to claim 14 in which said the invention is not limited thereto, but that it pressure is 1500 atmospher is desired to claim this invention as broadly as 16. A rubber-dike plastic product comprising thle plriicg1 art permits. essentially the reaction product, of sulfur and a 1. The process of preparing c re in e yis obtained by the copolymerization of a mixture physical characteristics ranging from those of a essentially the reaction product of sulfur and a viscous liquid to a plastic solid, and thereafter solid unsaturated polymerized hydrocarbon which heating said interpolymer with a sulfur. is obtained by the copolymerization of a mixture Processor preparing cured linear aliphatic containing at least 75 mol per cent of ethylene hydrocarbon interpolymers comprising the step and about '25 mol per cent of butadiene at temof subjecting to interpolymerization conditions a peratures between room temperature and 400 C. mixture containing at least mol per cent of and under a pressure of more than 500 atmos- 

